Transmission control circuits



Oct. 11, 1932. L JONES ET AL 1,881,642

TRANSMISSION CONTROL CIRCUITS Filed July 15, 1931 FIG! AMI?

H.L.JON'S 'EAVEAZ/E BVm y a' ATTORNEY Patented Oct. 11, 1 932 uu lrunsrarss issrel'z PATENT oar-ice HERBERT L. JONES, OF MORRISTOWN, NEW JERSEY, AND EDMUND A. VEAZIE OF NEW YORK, N. Y., ASSIGNORS TO BELL TELEPHONE LABORATORIES, INCORPORATED, v v OFsNEW YORK, N. Y., A CORPORATION OF NEW YORK TRANSMISSION CONTROL CIRCUITS Application filed. July 15,

. This invention relates to circuits employing electric space discharge tubes and particularly gaseous or gas-filled space discharge The invention has particular application tosign'al transmission systems in' which the transmission characterlstics of the signal transmission paths are controlled by signals transmitted over the system. In systems of this typein the prior art 1t has been common to utilize a portion of the'spee'ch or other signaling energy transmitted over the system to control operation of an amplifiendetector circuit employing'high vacuum tubes. The ampl fier-detector circuit in turncontrols the actuation of electromagnetic relays or con-- trols directly a variable loss element assoiated'wlth a'signal transmission path,;so as to control the transmission efiiciency of the path in the desired manner. In systems of this character, among the important factors "determining the proper operation, there may be mentioned the operate time, sensitivity and uniformity of response'of the signaLoperated control; circuits. j Heretofore, it has been 'foundthat the use of gaseous discharge tubes in'connection with control circuits of the above mentioned type enables a more uniform response, a reduction in the operate time and a greater sensitiv ty tobe attained wlthout unduly complicating the circuits or increasing their cost.

An object oftheinvention is to improve 7 upon circuits employing gaseous electricidischarge tubes for transmission control and similar uses. A'related and more specific 'obj ect is to improve the construction and operatlon of signal-controlled apparatus 1n wh1ch gaseous tubes areused.

In one embodiment of the invention applied to a circuit for suppresslngechoes and preventing singing in atwo-way signal transjmi ssion system, the characteristics of a gasous electric discharge device comprising two anodes are employed to give the deslred control. The gaseous device is so connected to the signal transmission path as to 'actas a high impedance-shunt across the path normally and as a lowimpedance shunt when alternatingcontrol currents are applied to its in- 19a1. Serial No. 551,014.

put so as to cause ionization of the gas in the tube. In one modification, the alternating control currents are also impressed on the in put of an auxiliary three-electrode vacuum tube operating as a plate current detectorto control a relay which operates to apply a metallic short circuit on'the transmission path, and to disable the gaseous device. The detector tube maintains the short circuit on the signal transmission path until the .input voltage dropsbelow a critical value and then the circuit quickly restores to its normal condition.

In another modification of the invention, s11n1lar results are. obtained w1thout the use of the auxiliary three-electrode vacuum tube.

Theialternating control currents applied to the input of the gaseous device break down the gas so that the resulting low impedance path between the two anodes effectively shortcircuits the transmission path as before. The resulting plate current energizes the winding of a relay in the plate circuit, causing operation of the relay first to apply a metallic short circuit across the transmission path, and? then to modify the output circuit of the gaseous tube so that the tube will oscillate as long as the control currents are impressed substantially continuously on the input there- "of, and thirdly, to short-circuit a condenser which show portions of a four-wire repeating 'circuitequipped with echo suppressors embodylng different modifications of the invention. M Fig. 1 shows the invention embodied in a echo suppressor applied to a four-wire repeating circuit only a portion ofthe circuit a being shown. The four-wire repeating circuit comprises a one-way transmission path EA including the one-way amplifying device 1 for repeating signals in the direction from west to east, and the one-way transmission path includingthe one-Way amplifying device 2 for repeating signals in the direction from east to West. The one-Way amplifying paths EA and WA may be connected at each end in energy transmitting relation with the two-Way transmission circuits between which signals are to be repeated (not shown) and in substantial conjugate relation With each other by hybrid coil transformersand associate'd balancingnetivorks or by. any other suitable means. 7 I V .7 l V.

Branched across the path WA at any suitablep oint, for example, in theoutputf'of theamplifying device 2 therein,is the input circuit 3 of an echo suppressor comprising the -three-electrode vacuum tube amplifying deviced, and the gaseous electric discharge device 5. and the three-electrode space discharge f the amplifying device 4 through the inter- "St'agetransformer 7 V rThega fi l d vice 5' device 6 arranged to operate as aplate current detector, fed in parallel from the output comprises a tube (containing a small amount ofa" gas, such as largon afcathode or filament, acontrolelecv trode or} grid and two aetdesb tim The gasin the tube gives it apeculiar. grid-plate Current characteristic. As long as the potential of the-grid vvith respect to the cathode remains under a certain critical value,' which is usually about -l-b'zvglts, no'plate current -vvill fl w and the anode to anode impedance is veryhigh. HoWevenIas soon as the input voltageexceeds the cr t cal value t e tube 1 the .breaksdown, plate current starts to flow and anode to anode impedance of the tube becomes very low. I p ,The tWo anodes of the gaseous tubeb are 7 connected respectively to opposite sidesfof the transmission path Thefilaments of the 1 tubes 4, '5 and 6 are supplied'in series With heating current from the battery. 8. A suffi- *cient negative polarizing potential is'fapplied by battery-9 to the grid ofthe gaseous tube ethrough resistances l0 and 11 so thatthe tube 5"is'no'rmally in the inoperative condi- .tion, and therefore, the anode to anode impedance thereof connected across the path EA is so high as to have littleeifect-on the flow of signalsfover that path .7" Also, the rectifier tube 6 isnormal'ly maintainedin-- operative by anegative polarizing potential 'applied to the grid thereof by the battery 12 through the secondary Winding of interstage transformer 7.; Space current issupplied -by battery v13 to the. amplifying device 4 through the primary Winding of interstage transformer "7. Space current "is also suplied by the batteryl to thelplate ofthe rectifier tube6 through the right-handwvinding of-the mechanical relay 14, andto the tWo I anodes 'of device 5 through the lefthand lvvinding of relay 14', normally closed contacts l8yresistance 15",conductor 15; the respect ve halves ofthe prnnary W nding of transformer 16 in the path EA and the line wires of transmission path EA and the connection cuits of the gaseous tube 5.

. The operation of the circuit tvill nowbe described; 'When' signal transmission is ing place over the repeating path WA in the direction from easttovvest a portionofthe amplified signals in'the'outputofthe amplifying device 2 therein'passes into the input circuit 3 of the echo suppressor and is amplified bythe amplifying device 4 therein. The a mplifiedsignals-in.the output of the amplifying device 4 are impressed by interstage transformer 7 upon the input circuits ,of the gaseous tube 5 and therectifier tube 6 in parallel; The amplified'signal voltage impressed upon the input ,circuit of the gas- 5 eo'us tube 5 causes the gas therein to be ionized and thus the space path tojbecome conductive to transmit'space currentsubstantially instantaneously The anode to anode impedance: of the tube 5v isthus immediately reduced to a very low valueeffectivelyshortcircuiting the transmission path EA through the two anodes of. the tube 5 an'dthenew conf ductive space path therebetvv'een,

The amplified signalvoltage simultaneously impressed uponthe' input'circuit of ,the detector tubeIG by interstage transformer 7 causestube 6 to operate causing current to flow in the plate-filament circuit thereof through the right-hand Windingof relay 14:

so as to assist tube 5 in operating thatrelay.

Relay 14 operates first toclose normally open contacts 17 thus connecting the metallic short circuit 'across the transmission circuit EA;

Theoperationof relay 14 causes the normally'closed contacts 18in the conductor 15 to be opened slightly after the contacts 17 have been closed thus breaki'ng'the space cur rent supply circuit for tube 5. ,The'tube 5 Will then return to its normalcondition; that is, to the condition in which the anodeto. anode impedancethereof is high.- The characteristic non-self-restoring properties of the gas- 1 eous tubedoes not have the effectof making .the, echo suppressor non-restoring, WllQIltllB signal, input thereto ceases, for the gaseous tube 5 is only used toinitially suppress the .transmissionpath and'the tube 5 is1th'en allowedtoreturn to its normal condition when the metallic short circuit placed on the :path

lit)

'iinder control of detector tube 6. The suppression" of path 'IEA by the metallic short circuit is maintained under control of the three-electrode Vacuum tube detector tube 6.

."The plate-filament current of the detector tube 6 willmaintain the relay 14 operated as lon g as the amplified signal currents are being 7 substantially continuously impressed upon the input circuit of thetube. When trans- 1o missionwof signals over the path WA ceases "the amplified signal voltage applied to the input of the tube 6 will rapidly fall off. VJhen the input voltage to the tube '6 drops below pathEA is thereby broken and the plate-filament circuit of gaseous tube 5 closed. The restoration of the echo suppressor to its nor- V 'mal condition with the cessation of the control voltage thereto is rapid dueto the wellknown quick restoring characteristics of a three-electrode vacuum tube detector. The circuit is now in condition to be again actuated in responseto signal currents over the transmission path WA. I

V Fig. 2 shows a modification of the echo suppressor of Fig.1 which does not require the use of the additional vacuum tube for re-' r storing the circuit quickly to its normal condi- .35

anode-filament circuits of the gaseous tube 5, replaces the detector tube 6 and the relay 1 1 shown in the latterfigure. As in the case of the circuit of Fig. 1, the amplified signal voltage impressed on the input circuit of the gaseous tube 5 through interstage transformer? causestubeb to break down causing the path EA to be substantially instantaneously short-circuited through the low im- 1 pedance path between the anodes of the tube. V 'The resultant large plate current of tube 5 .flowing through the winding of relay 19 causes the operation of that relay to close normally open'contacts 20, 21 and 22 in order.

The closing of contacts 20 connectsa metallic short circuit across the transmission path EA. The closing of contacts 21 connects the circuit 23 between one anode and the filament its circuit of tube 5. The closing of contacts 22 short-circuits the condenser 26 normally in the grid-filament circuit of the gaseous tube 5. The circuit 23 may comprise a resistance 24 and condenser 25 of such value with respect to the constants of the circuits of the gaseous tube 5 as to form therewith an oscillatingcircuit thus maintaining relay 19 continuously energized and therefore contacts 20,

21 and 22 closed as long as the amplified signaling currents are impressed substantially continuously upon the input circuit of tube 5.

The short-circuiting of the. condenser 26 in the grid-filament circuit of the gaseous to its normally inoperative condition substantially instantaneously. 7 Although in the circuits of Fig. 1 and Fig. 2ronly the echo suppressor for suppressing the west to east amplifying'path EA when the signal currents are transmitted over the east to west amplifying-path l VA, has been shown, it is to be understood that another echo suppressor similar to that shown in Figs. 1 or 2 having its input connected across the amplifying path EA may be arranged tosuppress the amplifying path W' A when signal currents flow in the path EA. The suppressor circuits may be connected near the middle of the four-wire repeating circuit, at the terminals thereof, or at any other points.

p The circuits of the invention as illustrated and described employ a particular'tyoe of gaseous electric discharge device having two anodes for controlling the transmission charact'eristics of a signal transmission path as it has been found that such a device in operation does not produce objectionable click disturbances in associated telephone receivers. However, it is to be understood "that the invention is applicable as well to circuits employing other types of gaseous electric dischar e devices normally having a high impedance between the output electrodes which is changed to a low impedance when alternating currents are impressed on the input electrodes thereof, for example, the type of gaseous device disclosed in the copending application of G. H. Rockwood and W'. B. Lodge, Serial No. 514,931, filed Feb- "ruaryll, 1931. ther modifications which "may be made in the circuit of theinvention in shunt with said transmision circuit, and means automatically responsive to alterf nating current waves, receivedfrom said 1 .T edance of said device.

source for decreasingthe anode to anode im 2.1 In combination in a signal transmission system, two signal transmission paths, a: gasfilled electricspace discharge tube having input electrodes and a pair of anodes normally having a'highanode .to anode impedance, said anode to anode impedance being connected effectively in shunt with one of said p'aths, and means responsive to flow of signals "in r the other of said paths for applying a popair of anodes, connections from each anode to a differentside or" said path, said device normally having such a high anode to anode said relay; saidrelay being designedto release substantially instantaneously when theinput Voltage to. said vacuumItuloe-deviceialls below a critical Value.

1 7 The system of claim 3 and 1a wticmm last mentioned means comprises a relay in the anode c rcult of said gaseous device, and

operativelyresponsive to the current flowing V therein when said device is operated by the control waves applied to its input to apply and maintain a metallic shortcircuit across saidpath as long as said .controllwaves are substantially continuously supplied thereto,

al/ C1 to modify the circuit of said gaseous device so thatsaid device will be restored to its normal condition substantially simultaneouslywith cessation, in the supply of control waves-thereto.

I In witness iwhereof, we hereunto subscribe our names this 8th & 2nd days of July, 1931. HERBERT L." JONES.

EDMUND- V A; VEAZIE.

impedance as to: have little effect on the V transmission of signals over said means responsive to alternating current control Waves supplied to said circuit for operating 7 said device to soreduce the anode to anode impedance thereof as to efiiectively s'hort-cirunit said path, and means'also responsive v to said control waves for maintaining said path gshort-circuited during theduration ofsaid waves while conditioning thecontrol circuit a so that it will/return to its :normalcondition" 1 substantially instantaneously with cessation V of the supplyof control waves thereto.

, 4. Thesystem of claim 3 and in which the last mentioned means-comprises means responsive to the supplied alternating current control 'waves'for connecting a low impedance shunt across said path and for subsequently ncreasing the anode to anode 1mpedance ofisald gaseous devlce to its normal value, and. means'responsive' substantially 3v instantaneously to cessation in the supply of the control. wavesto said circuit for removing'said low impedance shunt fromsaidpath. '5. Thesystem of claim 3 and in which the when energized independently short-air cuit's said .pathand 'causesthe anode to anode im- 56 last mentioned means comprises a relay which i ,pedance of said gaseous device to be subs'e- 'quently ncreased to its normal value, and means responsive tosaid control Waves for ener iz'in vsai'd rela and res 'onsive sub-f1 'stantially instantaneously to cessation of f f said control wavesto deenerg-ize said relay.

- 6. The systemofoclaim 3-and 1n which the last mentioned means comprises a relay which when energized applies ametallic; short cir- 7 i cuit acrosssaid path and breaksthe anode j circuit ofsai'd gaseous device so as tor'estor-e 7 it to its normal condition, vacuum tube dc; -vice wsupplied with a portion of said control currents and.responsive thereto to energize l' 

